Transmission apparatus, reception apparatus, transmission method, and reception method of wireless communication system

ABSTRACT

A transmission apparatus according to an exemplary embodiment of the present invention comprises a serial/parallel (S/P) converter for converting an input bit stream into a plurality of symbols each including 3 bits, a differential modulator for generating differential encoded symbols by applying π/4 phase rotation to each of the symbols, up-samplers for up-sampling the differential encoded symbols, filters for filtering the up-sampled symbols, digital/analog (D/A) converters for converting the filtered symbols into analog signals, and a quadrature modulator for performing quadrature modulation on the converted analog signals.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2009-0113489 filed in the Korean IntellectualProperty Office on Nov. 23, 2009, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a transmission apparatus, a receptionapparatus, a transmission method, and a reception method of a wirelesscommunication system.

(b) Description of the Related Art

When a wireless communication system is designed, there is a growingdemand for high data communication speed, realization of low poweroperation, and good communication performance. Accordingly, the threedemands need to be sufficiently taken into consideration when a methodof processing signals in a transmission apparatus and a receptionapparatus of a wireless communication system is selected.

Meanwhile, to maintain precise timing synchronization in a wirelesscommunication system, a method of reducing a frequency offset between atransmission apparatus and a reception apparatus using a high precisioncrystal oscillator can be used. However, with a communication system,such as a Wireless Body Area Network (WBAN) for wireless communicationbetween an implant device within the human body and a device outside thehuman body, is not easy to adopt a precise crystal oscillator because ithas to be implemented with an ultra-small size and low power operation.

Further, in wireless communication with a synchronization method, theproblem of a frequency offset occurring when data are demodulated can besolved by providing a pilot channel for synchronization acquisition andrestoring an accurate frequency by estimating a frequency and a phaseoffset using a received pilot signal. The performance of such asynchronization reception method is greatly changed depending on howaccurately the frequency and the restored phase offset are.

In packet-based wireless communications, such as a Wireless PersonalArea Network (WPAN) and the WBAN, a method of estimating andcompensating for a frequency error using a preamble is used because itis difficult to additionally support the pilot channel. However, in areception method estimating synchronization using the preamble, adifference between a frequency offset that is actually applied and anestimated frequency offset generates a remaining frequency offset,thereby degrading the performance of a receiver.

A differential modulation/demodulation method can be used to implement areceiver in an asynchronization reception method performing modulationusing a phase difference between symbols and performing demodulationusing a phase difference between a previous symbol and a current symbol.Accordingly, the differential modulation/demodulation method can greatlyreduce the influence of performance degradation on a change in thefrequency offset occurring in the synchronization reception method.Further, the differential modulation/demodulation method is robust to aphase shift of a small range occurring between neighboring symbols, andit can reduce the effect of a phase noise. Moreover, an asynchronousreceiver using differential demodulation is advantageous in that it canbe simply realized and can greatly reduce complexity because additionalcircuits for channel estimation and compensation are not required.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide atransmission apparatus, a reception apparatus, a transmission method,and a reception method of a wireless communication system havingadvantages of improving the performance for a back-off characteristic ofa nonlinear element due to a sharp phase shift, preventing performancedegradation for a change in the frequency offset, and reducingcomplexity in a wireless communication system.

An exemplary embodiment of the present invention provides a transmissionapparatus including a serial/parallel (S/P) converter for converting aninput bit stream into symbol including 3 bits, a differential modulatorfor generating differential encoded symbols by applying π/4 phaserotation to each of the symbols, up-samplers for up-sampling thedifferential encoded symbols, filters for filtering the up-sampledsymbols, digital/analog (D/A) converters for converting the filteredsymbols into analog signals, and a quadrature modulator for performingquadrature modulation on the converted analog signals.

The differential modulator can place a symbol waveform in a front partwhen a first bit of the symbol is 0 and place the symbol waveform in arear part when a second bit of the symbol is 1.

The differential modulator generates a complex variable using second andthird bits of the symbol, and generates a current differential encodedsymbol by multiplying a previous differential encoded symbol and thecomplex variable. The differential modulator generates a complexvariable using second and third bits of the symbol, and generates thephase of a current differential encoded symbol by multiplying the phaseof a previous differential encoded symbol and the phase of the complexvariable. Here, the phase of an initial symbol is 0°.

The filter can comprise a square root raised cosine (SRRC) filter.

The filter has a time cycle that is half a cycle of the up-sampledsymbol, and can have a roll-off factor of 1 to minimize intra-symbolinterference.

Another exemplary embodiment of the present invention provides a methodof a transmission apparatus of a wireless communication systemtransmitting a signal, including receiving an input bit stream,converting the input bit stream into a plurality of symbols eachincluding 3 bits, generating differential encoded symbols by applyingπ/4 phase rotation to each of the symbols, up-sampling the differentialencoded symbols, filtering the up-sampled symbols, converting thefiltered symbols into analog signals, and performing quadraturemodulation on the converted analog signals and transmitting the result.

Generating the differential encoded symbols can include placing a symbolwaveform in a front part when a first bit of the symbol is 0, andplacing the symbol waveform in a rear part when a second bit of thesymbol is 1.

Generating the differential encoded symbols includes generating acomplex variable using second and third bits of the symbol, andgenerating a current differential encoded symbol by multiplying aprevious differential encoded symbol and the complex variable. Here, aninitial symbol can be 1.

Generating the differential encoded symbols includes generating acomplex variable using second and third bits of the symbol, andgenerating a phase of a current differential encoded symbol bymultiplying a phase of a previous differential encoded symbol and aphase of the complex variable. Here, the phase of an initial symbol canbe 0°.

Yet another exemplary embodiment of the present invention provides areception apparatus, including a comparator for receiving symbols, eachconfigured to include 3 bits and subject to differential encoding, andcomparing a magnitude of an even-numbered symbol and a magnitude of anodd-numbered symbol, a differential decoder for decoding any one of theeven-numbered symbols and the odd-numbered symbols, and aparallel/serial (P/S) converter for converting the decoded symbols inseries.

The comparator can determine a first bit of the 3 bits to be 1 when themagnitude of the even-numbered symbol is smaller than or equal to themagnitude of the odd-numbered symbol, and determine the first bit of the3 bits to be 0 when the magnitude of the even-numbered symbol is greaterthan the magnitude of the odd-numbered symbol.

The differential decoder can include symbol delay units for generatingdelayed symbols by delaying a symbol having a greater magnitude, fromamong the even-numbered symbol and the odd-numbered symbol, a conjugatecomplex multiplier for performing a conjugate complex multiplication oneach of the delayed symbols and the symbol having a greater magnitude,and signal detectors for decoding the respective conjugate complexmultiplication results.

The signal detector can determine second and third bits of the 3 bitsbased on the decoding results.

The reception apparatus can further include a quadrature demodulator forreceiving a differentiated symbol from a transmission apparatus andperforming quadrature demodulation on the differentiated symbol,analog/digital (A/D) converters for converting thequadrature-demodulated symbols into respective digital symbols, filtersfor filtering the converted digital symbols, and a synchronizer forsampling the filtered symbols and transmitting the sampling results tothe comparator.

Yet another exemplary embodiment of the present invention provides amethod of a reception apparatus of a wireless communication systemreceiving a signal, including comparing a magnitude of an even-numberedsymbol and a magnitude of an odd-numbered symbol from among symbols eachconfigured to include 3 bits and differentiated by applying π/4 phaserotation to each of the symbols, decoding a symbol having a greatermagnitude from among the even-numbered symbol and the odd-numberedsymbol, and converting the decoded symbols in series.

Comparing the magnitude of the even-numbered symbol and the magnitude ofthe odd-numbered symbol can include determining a first bit of the 3bits to be 1 when the magnitude of the even-numbered symbol is smallerthan or equal to the magnitude of the odd-numbered symbol, anddetermining the first bit of the 3 bits to be 0 when the magnitude ofthe even-numbered symbol is greater than the magnitude of theodd-numbered symbol.

Decoding the symbol having a greater magnitude can include generatingdelayed symbols by delaying the symbol having a greater magnitude fromamong the even-numbered symbol and the odd-numbered symbol, performing aconjugate complex multiplication on each of the delayed symbols and thesymbol having a greater magnitude, and decoding the conjugate complexmultiplication results.

Decoding the symbol having a greater magnitude can further includedetermining second and third bits of the 3 bits based on the decodingresults.

The reception method can further comprise receiving the differentialencoded symbol from a transmission apparatus and performing quadraturedemodulation on the differential encoded symbol, converting thequadrature-demodulated symbols into digital symbols, filtering theconverted digital symbols, and sampling the filtered symbols andtransmitting the sampling results.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a transmission apparatus of a wirelesscommunication system according to an exemplary embodiment of the presentinvention;

FIG. 2 is a diagram illustrating a method of the differential modulatorof the transmission apparatus according to an exemplary embodiment ofthe present invention modulating symbols into differential encodedsymbols;

FIG. 3 is a graph showing the transmission output of the transmissionapparatus according to a phase silence shift keying (PSSK) method usinga scatter diagram;

FIG. 4 is a graph showing the transmission output of the transmissionapparatus according to an exemplary embodiment of the present inventionusing a scatter diagram;

FIG. 5 is a graph showing the trajectory of an analog transmissionsignal of the transmission apparatus according to the PSSK method on acomplex plane using a signal trajectory diagram;

FIG. 6 is a graph showing the trajectory of an analog transmissionsignal of the transmission apparatus according to an exemplaryembodiment of the present invention on a complex plane using a signaltrajectory diagram;

FIG. 7 is a graph showing the output of an in-phase amplitude signal,from among the transmission signals of the transmission apparatusaccording to the PSSK method, using an eye diagram;

FIG. 8 is a graph showing the output of a quadrature amplitude signal,from among the transmission signals of the transmission apparatusaccording to the PSSK method, using an eye diagram;

FIG. 9 is a graph showing the output of an in-phase amplitude signal,from among the transmission signals of the transmission apparatusaccording to an exemplary embodiment of the present invention, using aneye diagram;

FIG. 10 is a graph showing the output of a quadrature amplitude signal,from among the transmission signals of the transmission apparatusaccording to an exemplary embodiment of the present invention, using aneye diagram;

FIG. 11 is a flowchart illustrating a transmission method of a wirelesscommunication system according to another exemplary embodiment of thepresent invention;

FIG. 12 is a block diagram showing a reception apparatus of a wirelesscommunication system according to yet another exemplary embodiment ofthe present invention;

FIG. 13 is a graph showing bit error rates (BERs) according to whitenoise of final signals that have been received and processed by severalconventional reception apparatuses and the reception apparatus accordingto the exemplary embodiment of the present invention; and

FIG. 14 is a flowchart illustrating a reception method of a wirelesscommunication system according to yet another exemplary embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following detailed description, only certain exemplaryembodiments of the present invention have been shown and described,simply by way of illustration. As those skilled in the art wouldrealize, the described embodiments may be modified in various differentways, all without departing from the spirit or scope of the presentinvention. Accordingly, the drawings and description are to be regardedas illustrative in nature and not restrictive. Like reference numeralsdesignate like elements throughout the specification.

In the entire specification, unless explicitly described to thecontrary, the word “comprise” and variations such as “comprises” or“comprising” will be understood to imply the inclusion of statedelements but not the exclusion of any other elements. In addition, theterms “-er”, “-or”, and “module” described in the specification meanunits for processing at least one function and operation and can beimplemented by hardware components or software components andcombinations thereof.

The transmission apparatus of a wireless communication system accordingto an exemplary embodiment of the present invention is described indetail below with reference to FIG. 1.

FIG. 1 is a block diagram showing the transmission apparatus of thewireless communication system according to the exemplary embodiment ofthe present invention.

Referring to FIG. 1, the transmission apparatus 100 according to theexemplary embodiment of the present invention includes a serial/parallel(S/P) converter 110, a differential modulator 120, up-samplers 131 and132, filters 141 and 142, digital/analog (D/A) converters 151 and 152,and a quadrature modulator 160.

The S/P converter 110 receives an input bit stream a_(n), and symbolizesthe input bit stream a_(n) into a plurality of symbols each including 3bits a_(p,n), a_(i,n), and a_(q,n). Accordingly, a relationship betweena time cycle T_(b) of the input bit stream a_(n) and a time cycle T_(s)of each of the symbols a_(p,n), a_(i,n), and a_(q,n) can be expressedusing the following Equation 1.T_(s)=3T_(b)   [Equation 1]

The differential modulator 120 receives the symbols a_(p,n), a_(i,n),and a_(q,n) and generates differential encoded symbols d_(n) by applyingπ/4 phase rotation to each of the symbols. This process is described indetail with reference to FIG. 2.

FIG. 2 is a diagram illustrating a method of the differential modulatorof the transmission apparatus according to an exemplary embodiment ofthe present invention modulating symbols into differential encodedsymbols.

Referring to FIG. 2, for example, if the input bit stream a_(n) inputtedto the S/P converter 110 is “010111100001111001100010”, the input bitstream a_(n) is converted into a plurality of the symbols a_(p,n),a_(i,n), and a_(q,n) each including 3 bits through the S/P converter 110and then output.

In the case in which the first bit a_(p,n) of each of the symbolsa_(p,n), a_(i,n), and a_(q,n) is “0”, the differential modulator 120places a symbol waveform in the front part F and a silence period in therear part R. In the case in which the first bit a_(p,n) of each of thesymbols a_(p,n), a_(i,n), and a_(q,n) is “1”, the differential modulator120 places the silence period in the front part F and the symbolwaveform in the rear part R. Further, the differential modulator 120generates a complex variable A_(n) by mapping the second bit a_(p,n) andthe third bit a_(i,n) of each of the symbols a_(p,n), a_(i,n), a_(q,n)to a gray-coded complex secondary plane having four phases. The complexvariable A_(n) has a phase ΔP_(n) for a phase shift. The phase can bedetermined as in the following Table 1.

TABLE 1 Pattern of (ai, n, aq, n) Complex variable A_(n) Phase ΔP_(n) 11 (1 + j)/{square root over (2)}  π/4 01  (1 − j)/{square root over (2)}−π/4 10 (−1 + j)/{square root over (2)} 3π/4 00 (−1 − j)/{square rootover (2)} −3π/4 

The phase ΔP_(n) according to the input bit stream a_(n) is determinedas shown in FIG. 2 in accordance with Table 1.

Further, the differential modulator 120 determines the differentialencoded symbols in accordance with the following Equation 2.d _(n) =d _(n-1) ·A _(n)   [Equation 2]

Assuming that a current differential encoded symbol is d_(n) and aprevious differential encoded symbol is d_(n-1), the currentdifferential encoded symbols d_(n) is determined by multiplying acurrent complex variable A_(n) and the previous differential encodedsymbol d_(n-1).

Here, the phase of an initial symbol is set to 0° (=1). Equation 2 canbe converted into the following Equation 3 according to a phaserelation.P _(n) =P _(n-1) ×P _(n)   [Equation 3]

That is, the differential modulator 120 generates a phase P_(n) of thecurrent differential encoded symbol by adding the phase ΔP_(n) of acomplex variable to a phase P_(n-1) of the previous differential encodedsymbol.

Referring back to FIG. 1, each of the up-samplers 131 and 132 up-samplesthe differential encoded symbol d_(n) L times.

The filters 141 and 142 are transmitted pulse shaping filters forlimiting the bands of up-sampled symbols d_(n) and are configured tooutput respective filtered signals d_(i,k) and d_(q,k). The filteredsignals d_(i,k) and d_(q,k) form a transmission signal form whileoverlapping with each other as shown in FIG. 2. The filters 141 and 142can be, for example, square root raised cosine (SRRC) filters. Althoughother filters than the SRRC filter can be used as the filters 141 and142, transmission filters capable of minimizing intra-symbolinterference can be used as the filters 141 and 142 because the amountof information is increased due to the orthogonality of the front partand the rear part within one symbol. A controlled roll-off factor β canbe used. Further, the time cycle of each of the filters 141 and 142 canbe a half cycle T_(p) of the symbol cycle T_(s) as in the followingEquation 4 rather than the symbol cycle T_(s).T _(p)=T_(s)/2   [Equation 4]

Assuming that the roll-off factor 13 for minimizing intra-symbolinterference is “1” and a shaping time cycle is T_(s)/2, the followingEquation 5 can be produced.

$\begin{matrix}\begin{matrix}{{p(t)} = {\frac{4\beta}{\pi\sqrt{T_{p}}}\frac{{\cos\left\lbrack {{\pi\left( {1 + \beta} \right)}{t/T_{p}}} \right\rbrack} + \frac{\sin\left\lbrack {{\pi\left( {1 - \beta} \right)}{t/T_{p}}} \right\rbrack}{4{\beta\left( {t/T_{p}} \right)}}}{\left\lbrack {1 - \left( {4\beta\;{t/T_{p}}} \right)^{2}} \right\rbrack}}} \\{{= {\frac{4\sqrt{2}}{\pi\sqrt{T_{s}}}\frac{\cos\left\lbrack {4\pi\;{t/T_{s}}} \right\rbrack}{\left\lbrack {1 - \left( {8{t/T_{s}}} \right)^{2}} \right\rbrack}}},\mspace{14mu}\left( {{\beta = 1},\mspace{14mu}{T_{p} = {T_{s}/2}}} \right)}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

The D/A converters 151 and 152 convert transmission shaping filteredsignals d_(i,k) and d_(q,k) into respective analog signals in accordancewith the following Equation 6.

$\begin{matrix}{{s(t)} = {\sqrt{2E_{b}}{\sum\limits_{k}{d_{k}{p\left( {t - {k\;{T_{s}/2}}} \right)}}}}} & \left\lbrack {{Equation}\mspace{14mu} 6} \right\rbrack\end{matrix}$

The analog signal s(t) has a form such as that shown in FIG. 2.

The quadrature modulator 160 performs quadrature modulation on theanalog signal s(t) and outputs the result.

The transmission outputs of the transmission apparatus according to someexemplary embodiments of the present invention are described in detailbelow with reference to FIGS. 3 to 10.

FIG. 3 is a graph showing the transmission output of the transmissionapparatus according to the PSSK method using a scatter diagram, and FIG.4 is a graph showing the transmission output of the transmissionapparatus according to an exemplary embodiment of the present inventionusing a scatter diagram.

Referring to FIG. 3, four constellation points can be checked on thespace in the transmission output of the transmission apparatus accordingto the PSSK method. Referring to FIG. 4, in the transmission output ofthe transmission apparatus according to the exemplary embodiment of thepresent invention, since the constellation points of a symbol aregenerated on the space in which a current symbol is rotated by π/4 in aprevious symbol, eight constellation points can be checked on the space.

FIG. 5 is a graph showing the trajectory of an analog transmissionsignal of the transmission apparatus according to the PSSK method on acomplex plane using a signal trajectory diagram, and FIG. 6 is a graphshowing the trajectory of an analog transmission signal of thetransmission apparatus according to an exemplary embodiment of thepresent invention on a complex plane using a signal trajectory diagram.

Referring to FIG. 5, the trajectory of an analog transmission signal ofthe transmission apparatus according to the PSSK method using the signaltrajectory diagram draws the trajectory of a diagonal direction to thetrajectory of a square. Here, since an abrupt phase shift of 180° isgenerated, a spectrum distortion resulting from a nonlinear element,such as an amplifier of a wireless frequency domain, can be generated.To compensate for the degraded nonlinear characteristic, the loss ofpower can be generated through back-off which is the operating region ofthe amplifier.

Referring to FIG. 6, in the trajectory of an analog transmission signalof the transmission apparatus according to the exemplary embodiment ofthe present invention, an abrupt phase shift of 180° is not generated,but a phase shift of a maximum of 135° is generated. Accordingly, theoccurrence of a spectrum distortion resulting from a nonlinear element,such as that in the analog transmission signal of a transmissionapparatus according to the PSSK method, can be prevented.

FIG. 7 is a graph showing the output of an in-phase amplitude (I)signal, from among the transmission signals of the transmissionapparatus according to the PSSK method, using an eye diagram. FIG. 8 isa graph showing the output of a quadrature amplitude (Q) signal, fromamong the transmission signals of the transmission apparatus accordingto the PSSK method, using an eye diagram. FIG. 9 is a graph showing theoutput of an I signal, from among the transmission signals of thetransmission apparatus according to an exemplary embodiment of thepresent invention, using an eye diagram. FIG. 10 is a graph showing theoutput of a Q signal, from among the transmission signals of thetransmission apparatus according to an exemplary embodiment of thepresent invention, using an eye diagram.

FIGS. 7 to 10 show signals that are restored by estimating an optimalsampling time of a maximum vertical eye opening in a receiver.

Referring to FIGS. 7 and 8, in accordance with the transmissionapparatus according to the PSSK method, each of the I signal and the Qsignal of the transmission output has three levels of about 0.5, 0, and−0.5. Meanwhile, referring to FIGS. 9 and 10, in accordance with thetransmission apparatus according to the PSSK method, each of the Isignal and the Q signal of the transmission output has four levels ofabout 1, 0.707, −0.707, and −1.

A transmission method of the transmission apparatus according to anotherexemplary embodiment of the present invention is described in detailbelow with reference to FIG. 11.

FIG. 11 is a flowchart illustrating a transmission method of a wirelesscommunication system according to another exemplary embodiment of thepresent invention.

First, the input bit stream a_(n) is received and symbolized into aplurality of symbols each including 3 bits at step S310.

The symbols are modulated into differential encoded symbols by applyingπ/4 phase rotation to each of the symbols at step S320. Here, theprocess of modulating the symbols into the differential encoded symbolsincludes placing a symbol waveform in the front part or the rear partaccording to the first bit of the symbol and generating a complexvariable by mapping the second and third bits of the symbol to agray-coded complex secondary plane having four phases. The complexvariable and a previous differential encoded symbol are multiplied toproduce a current differential encoded symbol. That is, a phase of acurrent differential encoded symbol is determined by adding a phase ofthe previous differential encoded symbol and a phase of the complexvariable. Here, the phase of the complex variable can be π/4, π/4, 3π/4,or −3π/4.

Next, the differential encoded symbols are up-sampled at step S330, andthe up-sampled signals are subject to transmitted pulse shapingfiltering at step S340.

Next, the filtered signals are converted into analog signals at stepS350, and the converted analog signals are subject to quadraturemodulation at step S360.

A reception apparatus of a wireless communication system according toanother exemplary embodiment of the present invention is described indetail below with reference to FIG. 12.

FIG. 12 is a block diagram showing the reception apparatus of thewireless communication system according to yet another exemplaryembodiment of the present invention.

Referring to FIG. 12, the reception apparatus 200 includes a quadraturedemodulator 210, analog/digital converters 221 and 222, filters 231 and232, a synchronizer 240, a comparator 250, symbol delay units 261 and262, a conjugate complex multiplier 263, signal detectors 264, 265, and266, and a parallel/serial (P/S) converter 270.

The signal s(t) transmitted by the transmission apparatus 100 includesnoise and a frequency error while passing through radio channels.Consequently, a signal r(t) received by the reception apparatus 200 canbe expressed using the following Equation 7.r(t)=e ^(jv(t)) s(t−τ)+n(t)   [Equation 7]

where 9(t) is a composed phase signal under the influence of mismatchresulting from a local oscillator error, and n(t) is complex Gaussianwhite noise having a power spectrum density of N_(o)/2.

The quadrature demodulator 210 performs quadrature demodulation on thereceived signal r(t), and corresponds to the quadrature modulator 160 ofthe transmission apparatus 100.

The A/D converters 221 and 222 convert the quadrature-modulated signalsinto respective digital signals.

The filters 231 and 232 are matching filters for receiving the converteddigital signals and outputting respective maximum output values of theinput signals. The same filters as the transmission pulse shapingfilters 141 and 142 of the transmission apparatus 100 can be used as thefilters 231 and 232.

The synchronizer 240 acquires timing synchronization and an initialphase offset and then samples the output signals of the filters 231 and232 at time intervals of T_(s)/2. Here, a complex expression equation ofthe sampled and averaged signals is as shown in the following Equation8.r _(k) =e ^(j{2πkΔf(T) ^(s) ^(/2)+θ}) s _(k) +n _(k)   [Equation 8]

where Δf is a factor resulting from the influence of a carrier frequencyoffset, and θ is an initial phase offset uniformly distributed from 0 to2p.

The comparator 250 receives output signals r_(i,k) and r_(q,k) from thesynchronizer 240 and finds the magnitudes of the signals based onabsolute values of the signals, acquired using the following Equation 9,and then compares the magnitude of an even-numbered signal r_(2k) andthe magnitude of an odd-numbered signal r_(2k+1).|r _(2k)|=√{square root over (r _(i,2k) ² +r _(q,2k) ²)}|r _(2k+1)|=√{square root over (r _(i,2k+1) ² +r _(q,2k+1)²)}  [Equation 9]

The even-numbered signal r_(2k) corresponds to the front part F of asymbol, and the odd-numbered signal r_(2k+1) corresponds to the rearpart R of the symbol.

If, as a result of the comparison, the magnitude of the even-numberedsignal r_(2k) is smaller than or equal to the magnitude of theodd-numbered signal r_(2k+1) as in the following Equation 10, thecomparator 250 determines the first bit z_(p,n) of a demodulation signalto be “1” because the waveform of the signal is placed in the rear partR of the symbol. However, if, as a result of the comparison, themagnitude of the even-numbered signal r_(2k) is greater than themagnitude of the odd-numbered signal r_(2k+1) as in the followingEquation 10, the comparator 250 determines the first bit z_(p,n) of thedemodulation signal to be “0”.

$\begin{matrix}{z_{p,k} = \left\{ {\begin{matrix}{1,} & {{r_{2k}} \leq {r_{{2k} + 1}}} \\{0,} & {{r_{2k}} > {r_{{2k} + 1}}}\end{matrix},\mspace{14mu}{k = 0},1,2,{{\ldots\mspace{14mu} K} - 1}} \right.} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

Further, the comparator 250 determines a signal having a greatermagnitude, from among the symbols r_(n), in accordance with thefollowing Equation 11.

$\begin{matrix}{r_{n} = \left\{ \begin{matrix}{r_{2k},} & {{r_{2k}} > {r_{{2k} + 1}}} \\{r_{{2k} + 1},} & {{r_{2k}} \leq {r_{{2k} + 1}}}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 11} \right\rbrack\end{matrix}$

A differential decoder 260 receives the symbols r_(n) from thecomparator 250 and performs differential decoding on the receivedsymbols r_(n). The differential decoder 260 includes the symbol delayunits 261 and 262, the conjugate complex multiplier 263, and the signaldetectors 264, 264, and 266.

The symbol delay units 261 and 262 generate delayed symbols r_(n-1) bydelaying the symbols r_(n) determined by the comparator 250. Theconjugate complex multiplier 263 acquires an inter-symbol phasedifference by performing a conjugate complex multiplication on thesymbols r_(n) and the delayed symbol r_(n-1). The signal detector 264receives the first bit z_(p,n) from the comparator 250 and finallydecodes and outputs the received first bit z_(p,n). The signal detectors265 and 266 receive the conjugate complex multiplication results w_(i,n)and w_(q,n), finally decode the conjugate complex multiplication resultsw_(i,n) and w_(q,n) in accordance with a demodulation table, such asthat shown in Table 2, and output respective decoded signals z_(i,n) andz_(q,n).

TABLE 2 Signs of conjugate complex multiplication results w_(i, n) andw_(q, n) Decoded signals z_(i, n), z_(q, n) +, + 11 +, − 01 −, + 10 −, −00

The operation of the differential decoder 260 described as above can beexpressed using the following Equation 12.

$\begin{matrix}\begin{matrix}{w_{n} = {r_{n} \cdot r_{n - 1}^{*}}} \\{= {{s_{N}s_{n - 1}^{*}{\mathbb{e}}^{{j2\pi\Delta}\;{fT}_{s}}} + {n_{n}s_{n - 1}^{*}{\mathbb{e}}^{({{{- {{j2\pi}{({n - 1})}}}\Delta\;{fT}_{s}} + \theta})}} +}} \\{{s_{n}n_{n - 1}^{*}{\mathbb{e}}^{({{{j2\pi}\; n\;\Delta\;{fT}_{s}} + \theta})}} + {n_{n}n_{n - 1}^{*}}} \\{= {{{\mathbb{e}}^{j{({\phi_{n} - \phi_{n - 1}})}} \cdot {\mathbb{e}}^{{j2\pi\Delta}\;{fT}_{s}}} + {I(n)}}} \\{= {w_{i,n} + {j\; w_{q,n}}}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

wherein I_(n) refers to mixed complex noise.

The P/S converter 270 receives the decoded signals z_(p,n), z_(i,n), andz_(q,n) (i.e., the first, second, and third bits of the symbol),converts the received signals in series, and outputs the result as afinal signal z_(n).

The performance of the reception apparatus according to an exemplaryembodiment of the present invention is described in detail below withreference to FIG. 13.

FIG. 13 is a graph showing the bit error rates (BERs) according to thewhite noise of final signals that have been received and processed byseveral conventional reception apparatuses and the reception apparatusaccording to the exemplary embodiment of the present invention.

FIG. 13 shows theoretical numerical values of the BERs according to thewhite noise of final signals, processed by the reception apparatusesaccording to an 8-Phase shift keying (8PSK) method, a quadrature PSK(QPSK) method, a differential QPSK (DQPSK) method, and an 8PSSK method.The BER according to the white noise of the final signal processed bythe reception apparatus using the 8PSSK method is drawn on the basis ofthe theory of 1.5 ppm when the frequency offset is 0 ppm. The BERaccording to the white noise of the final signal processed by thereception apparatus 100 according to the exemplary embodiment of thepresent invention is drawn on the basis of the theory of 40 ppm (8DPSSK)when the frequency offset is 0 ppm.

The gain of the 8PSSK method is 5.4 dB more than that of the 8PSK methodand about 1.2 dB more than that of the QPSK method, when the BER is10⁻⁶. However, in the case of the 8PSSK method, the influence on theremaining frequency offset remains 1.5 ppm, the performance is greatlydegraded, and so a great performance degradation of 6 dB or more isgenerated. The gain of the reception apparatus according to theexemplary embodiment of the present invention is about 1.7 dB smallerthan that of the reception apparatus using the 8PSSK method, but about1.7 dB greater than that of the reception apparatus using the DQPSKmethod which is a differential method. Accordingly, the receptionapparatus according to the exemplary embodiment of the present inventioncan have a stable performance in which performance degradation is within0.5 dB in a frequency offset within ±40 ppm when the frequency offset isgreat.

A reception method of a wireless communication system according toanother exemplary embodiment of the present invention is described indetail below with reference to FIG. 14.

FIG. 14 is a flowchart illustrating the reception method of the wirelesscommunication system according to yet another exemplary embodiment ofthe present invention.

Referring to FIG. 14, the quadrature demodulator 210 of the receptionapparatus 200 of the wireless communication system performs quadraturedemodulation on a signal r(t) received from the transmission apparatus100 at step S410.

The A/D converters 221 and 222 of the reception apparatus 200 receivethe quadrature-demodulated signals and convert the received signals intodigital signals at step S420.

The matching filters 231 and 232 filter the converted digital signalsand output maximum output values at step S430.

The synchronizer 240 samples the filtered signals at time intervals ofT_(s)/2 at step S440.

The comparator 250 receives the sampled signals and determines a firstbit forming a symbol at step S450. That is, the comparator 250 finds themagnitude of the signal by finding an absolute value of the sampledsignal and determines the first bit of the symbol by comparing themagnitude of an even-numbered signal and the magnitude of anodd-numbered signal, of the sampled signal.

The differential decoder 260 receives the sample signals and determinesthe second and third bits by performing differential decoding on thereceived sampled signals at step S460. That is, the differential decoder260 performs a conjugate complex multiplication on a delayed signal andthe signal determined by the comparator 250 to have a greater magnitude,from among the even-numbered signal and the odd-numbered signal, andperforms differential decoding using the conjugate complexmultiplication.

The parallel-serial converter 270 receives the first bit from thecomparator 250 and the second and third bits from the differentialdecoder 260, converts the first, second, and third bits into a serialsignal, and outputs a final signal.

In accordance with some exemplary embodiments of the present invention,in a wireless communication system, a 180° phase shift between symbolscan be fundamentally prevented using π/4 phase rotation. Accordingly,the transmission apparatus and the reception apparatus can beimplemented to be able to improve the back-off characteristic of anonlinear element and that are robust to a frequency offset and afrequency shift through a relatively simple asynchronous receiver andthat do not require circuits for channel estimation and compensation.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A transmission apparatus, comprising: aserial/parallel (S/P) converter for converting an input bit stream intosymbols comprising 3 bits; a differential modulator for generatingdifferential encoded symbols by applying π/4 phase rotation to each ofthe symbols; up-samplers for up-sampling the differential encodedsymbols; filters for filtering the up-sampled symbols; digital/analog(D/A) converters for converting the filtered symbols into analogsignals; and a quadrature modulator for performing quadrature modulationon the converted analog signals, wherein the differential modulatorplaces a symbol waveform in a front part when a first bit of the symbolis 0 and places the symbol waveform in a rear part when a second bit ofthe symbol is
 1. 2. A transmission apparatus, comprising: aserial/parallel (S/P) converter for converting an input bit stream intosymbols comprising 3 bits; a differential modulator for generatingdifferential encoded symbols by applying π/4 phase rotation to each ofthe symbols; up-samplers for up-sampling the differential encodedsymbols; filters for filtering the up-sampled symbols; digital/analog(D/A) converters for converting the filtered symbols into analogsignals; and a quadrature modulator for performing quadrature modulationon the converted analog signals, wherein the symbol comprises a firstbit and the differential modulator generates a complex parameter usingsecond and third bits of the symbol and generates a current differentialencoded symbol by multiplying a previous differential encoded symbol andthe complex parameter, wherein an initial symbol is
 1. 3. A transmissionapparatus, comprising: a serial/parallel (S/P) converter for convertingan input bit stream into symbols comprising 3 bits; a differentialmodulator for generating differential encoded symbols by applying π/4phase rotation to each of the symbols; up-samplers for up-sampling thedifferential encoded symbols; filters for filtering the up-sampledsymbols; digital/analog (D/A) converters for converting the filteredsymbols into analog signals; and a quadrature modulator for performingquadrature modulation on the converted analog signals, wherein thesymbol comprises a first bit and the differential modulator generates acomplex parameter using second and third bits of the symbol andgenerates a phase of a current differential encoded symbol bymultiplying a phase of a previous differential encoded symbol and aphase of the complex parameter, wherein a phase of an initial symbol is0°.
 4. A method of a transmission apparatus of a wireless communicationsystem transmitting a signal, the method comprising: receiving an inputbit stream; converting the input bit stream into a plurality of symbolseach comprising 3 bits; generating differential encoded symbols byapplying π/4 phase rotation to each of the symbols; up-sampling thedifferential encoded symbols; filtering the up-sampled symbols;converting the filtered symbols into analog signals; and performingquadrature modulation on the converted analog signals and transmittingthe result, wherein generating the differential encoded symbolscomprises placing a symbol waveform in a front part when a first bit ofthe symbol is 0 and placing the symbol waveform in a rear part when asecond bit of the symbol is
 1. 5. A method of a transmission apparatusof a wireless communication system transmitting a signal, the methodcomprising: receiving an input bit stream; converting the input bitstream into a plurality of symbols each comprising 3 bits; generatingdifferential encoded symbols by applying π/4 phase rotation to each ofthe symbols; up-sampling the differential encoded symbols; filtering theup-sampled symbols; converting the filtered symbols into analog signals;and performing quadrature modulation on the converted analog signals andtransmitting the result, wherein the symbol comprises a first bit andgenerating the differential encoded symbols comprises: generating acomplex parameter using second and third bits of the symbol, andgenerating a current differential encoded symbol by multiplying aprevious differential encoded symbol and the complex parameter, whereinan initial symbol is
 1. 6. A method of a transmission apparatus of awireless communication system transmitting a signal, the methodcomprising: receiving an input bit stream; converting the input bitstream into a plurality of symbols each comprising 3 bits; generatingdifferential encoded symbols by applying π/4 phase rotation to each ofthe symbols; up-sampling the differential encoded symbols; filtering theup-sampled symbols; converting the filtered symbols into analog signals;and performing quadrature modulation on the converted analog signals andtransmitting the result, wherein the symbol comprises a first bit andgenerating the differential encoded symbols comprises: generating acomplex parameter using second and third bits of the symbol, andgenerating a phase of a current differential encoded symbol bymultiplying a phase of a previous differential encoded symbol and aphase of the complex parameter, wherein a phase of an initial symbol is0°.